Recently, magnetic recording media have been required to be more sensitive. If magnetic recording medium is made more sensitive, a high quality image as well as a good sound quality and high density recording thereof can be realized. Those improvements can be attained by improving a magnetic recording and replaying system for a magnetic recording medium, and also improving a magnetic recording medium itself.
A magnetic recording medium can be more highly sensitized by increasing the signal and decreasing the noise, i.e., by increasing the signal/noise ratio itself. The signal can be increased by increasing the residual magnetic flux density and the coercive force of the magnetic recording medium, which can be realized by making ferromagnetic particles finer or adjusting the shape of anisotropy and arrangement of magnetic domains for each of the ferromagnetic fine particles.
The noise can be decreased by various factors, for example, by smoothing the magnetic layer and controlling the charging properties of the magnetic recording medium. It has been disclosed that a backing layer can be provided in order to control the charging properties of the magnetic recording medium and maintain the running durability thereof, for example, in Japanese Patent Publication Nos. 3927/75 and 23647/83, and Japanese Patent Application (OPI) Nos. 111828/82, 102004/77, and 96505/77 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
However, a magnetic recording medium having high sensitivity and sufficient running durability cannot be obtained satisfactorily by the above technology, because: (1) although spacing loss between the magnetic recording and replaying head and the magnetic recording medium can be reduced by smoothing the surface of the magnetic recording medium, the running durability thereof deteriorates and the friction coefficient increases, whereby the magnetic recording layer and the backing layer tend to wear out more quickly; (2) if the surface of the backing layer is made rough in order to improve the running durability of the backing layer, the rough surface of the backing layer is printed through on the magnetic layer before calendering treatment is conducted, whereby the signal/noise ratio of the magnetic layer decreases; (3) even at an early stage of running when the magnetic layer and the backing layer are not yet worn out, dropouts increase, thereby decreasing the signal/noise ratio; and (4) although calendering treatment can be conducted, as disclosed, for example, in Japanese Patent Publication No. 10244/74, to smooth a magnetic layer and to realize a highly sensitive magnetic layer, highly smoothening a magnetic layer to make it more sensitive also renders the backing layer smooth, whereby the backing layer easily drops off as a powder, and it is difficult to manufacture a magnetic recording medium having such a highly smoothed magnetic layer.